The heptadecapeptide orphanin FQ(OFQ)is a recently discovered neuropeptide that exhibits structural features reminiscent of the opioid peptides and that is an endogenous ligant to a G protein-coupled receptor sequentially related to the opioid receptors.OFQ was originally isolated from brain,but the presence of OFQ in peripheral tissues,especially in cardiovascular system,has not been clarified.The present study was designed to investigate the peripheral tissue distribution of OFQ precusor Mrna in stroke-prone spontaneously hypertensive rats(SHRSP)and compare the difference of OFQ precusor Mrna expression in aorta or cultured vascular smooth muscle cells(VSMCs)between SHRSP and wistar-Kyoto normotensive(WKY)rats.By using quantitative reverse transcription-polymerase chain reaction(RT-PCR),OFQ precusor Mrna was detected in aorta and ovary at high levels comparable with the amounts found in brain.Moderate expression was found in testis,while a little OFQ precusor Mrna could be detected in atrium.All other peripheral tissues examined from SHRSP,including ventricle,liver,lung and kidney,showed no expression of OFQ precusor Mrna.In the vascular system,OFQ precusor Mrna was expressed in aorta,pulmonary artery,renal artery and vein at high levels comparable with the amounts found in brain.We also found that OFQ precusor Mrna levels were much higher in aorta or cultured VSMCs from SHRSP than those from WKY rats.In conclusion,the present study has shown that OFQ precusor Mrna is present in some peripheral tissues,especially in cardiovascular and reproductive system,suggesting that OFQ possibly involves in the regulation of cardiovascular and reproductive functions.